# std::filesystem::directory_entry::is_block_file

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< cpp‎ | filesystem‎ | directory entry

bool is_block_file() const; | (1) | (since C++17)
bool is_block_file( std::error_code& ec ) const noexcept; | (2) | (since C++17)

Checks whether the pointed-to object is a block device. Effectively returns:

1) std::filesystem::is_block_file(status()).
2) std::filesystem::is_block_file(status(ec)).

### Parameters

ec | - | out-parameter for error reporting in the non-throwing overload

### Return value

true if the referred-to filesystem object is a block device, false otherwise.

### Exceptions

Any overload not marked `noexcept` may throw std::bad_alloc if memory allocation fails.

1) Throws std::filesystem::filesystem_error on underlying OS API errors, constructed with p as the first path argument and the OS error code as the error code argument.
2) Sets a std::error_code& parameter to the OS API error code if an OS API call fails, and executes ec.`clear`() if no errors occur.

### Example

Run this code

    #include <cstdio>
    #include <cstring>
    #include <filesystem>
    #include <fstream>
    #include <functional>
    #include <iostream>
    #include <memory>
    #include <sys/socket.h>
    #include <sys/stat.h>
    #include <sys/un.h>
    #include <unistd.h>

    namespace fs = std::filesystem;

    void print_entry_type(const std::filesystem::directory_entry& entry)
    {
        std::cout << entry.path() << ": ";

        if (!entry.exists())
            std::cout << "does not exist ";
        if (entry.is_block_file())
            std::cout << "is a block device ";
        if (entry.is_character_file())
            std::cout << "is a character device ";
        if (entry.is_directory())
            std::cout << "is a directory ";
        if (entry.is_fifo())
            std::cout << "is a named IPC pipe ";
        if (entry.is_regular_file())
            std::cout << "is a regular file ";
        if (entry.is_socket())
            std::cout << "is a named IPC socket ";
        if (entry.is_symlink())
            std::cout << "(a symlink)";
        if (entry.is_other())
            std::cout << "(an `other` file)";

        std::cout << '\n';
    }

    template<typename Type, typename Fun>
    class scoped_cleanup
    {
        std::unique_ptr<Type, std::function<void(const Type*)>> u;

    public:
        scoped_cleanup(Type* ptr, Fun fun) : u{ptr, std::move(fun)} {}
    };

    int main()
    {
        // Create files of different kinds.
        std::filesystem::current_path(fs::temp_directory_path());
        const std::filesystem::path sandbox{"sandbox"};
        scoped_cleanup remove_all_at_exit{&sandbox, [](const fs::path* p)
        {
            std::cout << "cleanup: remove_all(" << *p << ")\n";
            fs::remove_all(*p);
        }};
        std::filesystem::create_directory(sandbox);
        std::ofstream{sandbox/"file"}; // Creates a regular file
        std::filesystem::create_directory(sandbox/"dir");

        mkfifo((sandbox/"pipe").string().data(), 0644);
        struct sockaddr_un addr; addr.sun_family = AF_UNIX;

        std::strcpy(addr.sun_path, (sandbox/"sock").string().data());
        int fd{socket(PF_UNIX, SOCK_STREAM, 0)};
        scoped_cleanup close_socket_at_exit{&fd, [](const int* f)
        {
            std::cout << "cleanup: close socket #" << *f << '\n';
            close(*f);
        }};
        bind(fd, reinterpret_cast<sockaddr*>(std::addressof(addr)), sizeof addr);

        fs::create_symlink("file", sandbox/"symlink");

        for (std::filesystem::directory_entry entry: fs::directory_iterator(sandbox))
            print_entry_type(entry);

        // Request file system objects status directly:
        for (const char* str : {"/dev/null", "/dev/cpu", "/usr/include/c++",
                                "/usr/include/asm", "/usr/include/time.h"})
            print_entry_type(fs::directory_entry{str});

    } // Cleanup via scoped_cleanup objects

Possible output:

    "sandbox/symlink": is a regular file (a symlink)
    "sandbox/sock": is a named IPC socket (an `other` file)
    "sandbox/pipe": is a named IPC pipe (an `other` file)
    "sandbox/dir": is a directory
    "sandbox/file": is a regular file
    "/dev/null": is a character device (an `other` file)
    "/dev/cpu": does not exist
    "/usr/include/c++": is a directory
    "/usr/include/asm": is a directory (a symlink)
    "/usr/include/time.h": is a regular file
    cleanup: close socket #3
    cleanup: remove_all("sandbox")

### See also

is_block_file (C++17) | checks whether the given path refers to block device (function)

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